Manufacture of molded articles from coal



Patented Apr. 5, 1949 2,466,435 RIANUFACTURE 9F MQLDED ARTICLES FlttDlViCAL No Drawing.

Application July 30, 1945, Serial No. 667,910. in Great Britain August17, 1944 3 Claims.

In United States Patent application Serial No. 492,968, now U. S. PatentNo. 2,404,208, is described the manufacture of moulded articles fromcoal by subjecting an intimate mixture of certain finely comminutedbituminous coals and a softening agent in a mould to a pressure of atleast about 256 atmospheres at a temperature which is at least 256 C.and, under the pressure used, lies between the temperature at which themixture as a whole begins to soften and that at which it undergoesintumescence. Certain filling materials may, if desired, be incorporatedwith the coal-softening agent mixture to be moulded. Articles mouldedfrom the coal-softening agent mixture alone appear to the eye to have ahomogeneous and non-porous structure, and they have a conchoidalfracture, and do not produce a black streak when rubbed on paper.

Owing to the incorporation of the softening agent with the coal, it ispossible to use coals which, when heated alone, only begin to soften ator near the temperature of the onset of intumescence. This is due to thefact that the coal-softening agent mixture softens at a lowertemperature than does the coal when heated alone, and that theintumescence temperature of the mixture, as compared with that of thecoal alone, either is not lowered or is lowered to a much less extentthan the softening temperature is lowered.

We have now found that it is possible with mixtures of certain finelydivided coals and modifiers as hereinafter defined to obtain mouldedarticles which are especially stable to organic solvents, and to reducethe temperature and time of moulding, if the mixture is subjected to apreliminary briquetting and heat treatment as hereinafter described.

According to this invention a process for making moulded articlescomprises preparing an intimate mixture of finely divided coal having anagglutinating value greater than zero and as a modifier a, finelydivided coal tar pitch having a melting point of at least 110 C. in aproportion such that the coal-modifier mixture softens at a temperaturelower than does the coal when heated alone and not exceeding about 25per cent. of the combined weight of the coal and modifier, briquettingthe resulting mixture, heating the briquettes at a non-carbonizingtemperature ranging from 250 C. to 400 C. for at least one hour untiltheir content of constituents extractable by toluene is at most about 22per cent. based on the weight of the modifier, disintegrating theheat-treated briquettes, subjecting the disintegrated material in amould to a pressure of at least about 250 atmospheres at a temperatureat which under the pressure used the mixture softens as a whole withoutundergoing intumescence, and then slowly cooling the moulded article.

The expression agglutinating value greater than zero has reference tothe agglutinating value as determined by the method described in Britishstandards specification No. 705, 1936, and. the expression content ofconstituents extractable by toluene refers to the extraction testhereinafter described for determining the fixation of toluene-solubleconstituents; and it is in these senses that the foregoing expressionsare to be interpreted in the appended claims.

The disintegrated heat-treated briquettes may be subjected in the mouldto a pressure of 250- 260 atmospheres. The cooling of the mouldedarticle should be sufficiently slow to avoid the formation of cracks inthe article.

The relative proportions of the coal and modifier may be varied,provided that the proportion of the modifier does not exceed about 25per cent. of the combined weight of the coal and modifier, and is notbelow the proportion at which it is capable of acting as a modifier,that is to say, not below the proportion required to yield a mouldingcomposition which will soften without undergoing intumescence under thepressure used for moulding; and it is in this sense that the words as amodifier are used herein and in the appended claims. Generally speakinga suitable proportion of modifier is from about 18 to 25 per cent.calculated on the basis above mentioned.

The articles moulded from the disintegrated heat-treated briquettesalone are free from bubble structure, give a conchoidal fracture, are ofvery low electrical conductivity, and have a good resistance to acidsand alkalies.

The fixation of toluene-soiuble constituents in the heat-treatedbriquette or moulded articles as measured by the content of constituentsextractable by toluene is determined by the following extraction test:

A heat-treated briquette or moulded article is crushed and sievedthrough a 120 mesh B. S. S. sieve. 1 gram of the crushed sample isplaced in a small dry Soxhle't thimble, which is then closed with a plugof cotton wool, and the whole is weighed. The sample in the pluggedthimble is extracted with toluene in a Soxhlet extraction apparatusuntil colour is no longer imparted to the toluene. The thimble is thenremoved and dried at C. until its weight becomes constant. Thepercentage of material extracted based on the Weight of the modifier inthe pretreated mixture is calculated by the method described in B. S. S.No. 771, 1938, appendix B.

In the moulded articles made by the invention the degree of fixation ofthe toluene-soluble constituents is somewhat higher than that of the 3heat-treated briquettes from which the moulded articles are made.

It is important that the coal and modifier to be subjected to thepretreatment should be in a suificiently intimate state of contact toensure that substantially all the coal particles including the finestsizes are in contact with the modifier or are coated with a film of thelatter. Under these circumstances the assimilation of the modifier intothe coal substance during the heat treatment proceeds evenly throughoutthe mixture. In general a satisfactory state of sub-division of the coalis obtained by grinding it sufficiently to pass a 240 mesh B. S. S.sieve.

The coal tar pitch should have a melting point below the temperature ofthe heat treatment. There may be used, for example, coal tar pitcheswhose melting points are within the range of 110 C. to 210 C. We havefound that the higher the melting point of the pitch, for example,pitches having melting points of approximately 180 C., the better is thefixation of the toluenesoluble constituents under the same conditions ofheat treatment, for example, at 330 C. for 5 hours. In order to keep thetemperature low in the moulding operation it is desirable that thecontent of free carbon of the pitch should not exceed about 50 per cent.

Improved mechanical properties in the moulded articles may be obtainedby incorporating with the coal-modifier mixture prior to the heattreatment or with the disintegrated heat-treated briquettes fillingmaterials, for example, those described in United States patentapplication Serial No. 492,968. There may also be used fillers whichimpart a desired colour or lustre to the moulded article, for examplealuminium powder or copper bronze powder. Surface finishes may also beobtained in known manner by the use of powder, sheets or gauzes appliedto the mould.

In order to assist the flow of the composition during moulding, theremay be incorporated with the coal-modifier mixture prior to the heattreatment, or with the disintegrated heat-treated briquettes polymerisedmethyl methacrylate, which does not decompose at the pretreatmenttemperature or, if incorporated subsequently to the pretreatment, at themoulding temperature.

The moulded articles made in accordance with the invention may besubjected to a subsequent heat treatment in a non-oxidising atmosphere,for example, at temperatures up to 800 C., in order to increase theirdensity and impart electrical conductivity thereto, which properties maybe desirable for certain uses of the articles.

The following example illustrates the invention, the parts being byweight:

40 parts of a South Wales coking coal (having an agglutinating value of30, a volatile matter content of 25 per cent, and swelling number of 9as determined by B. S. S. 1016) ground to pass a 240 mesh B. S. S.sieve, 10 parts of coal tar pitch of melting point 120 C. from ahorizontal coke oven, and 50 parts of a mixture of equal parts of stonedust and asbestos powder (which mixture has been Well dried by heatingit to at least the moulding temperature) are thoroughly mixed togetherin a ball mill for /2 hour. The mixture is then briquetted at 100- 120C. under a pressure of /2 ton per square inch. The briquettes are thenheated in an oven to a temperature of 330 0., preferably in anonoxidising atmosphere, and maintained at that temperature for onehour. The briquettes are then ground in a ball mill to pass a mesh B. S.S. sieve, and during the grinding 4 per cent of polymerised methylmethacrylate calculated on the weight of the final mixture is added. Thelatter substance may be added in a very finely powdered form or in theform of a solution in benzene.

The ground material is then introduced into a mould which is heated to250 C. It is subjected in the mould to a pressure of 450 atmospheres at250 C. for 5 minutes. The moulded article is ejected from the mould andallowed to cool slowly at a rate of not more than 3 degrees centigradeper minute until its temperature is C. The further cooling may be rapid,if desired. The moulded article has a tensile strength of not less thanton per square inch. The percentage of toluene-soluble constituentscapable of extraction from a crushed sample of the moulded article bythe test hereinbefore described is 10.9 based on the weight of the pitchused.

We claim:

1. A process for making moulded articles, which comprises preparing anintimate mixture of finely divided coal having an agglutinating valuegreater than zero and as a modifier a finely divided coal tar pitchhaving a melting point of at least 110 C. in a proportion such that thecoal modifier mixture softens at a temperature lower than does the :coalwhen heated alone and not exceeding about 25 per cent. of the combinedweight of the coal and pitch, briquetting the resulting mixture, heatingthe briquettes at a non-carbonising temperature ranging from 250 C. to400 C. for at least one hour until their content of constituentsextractable by toluene is at most about 22 per cent. based on the Weightof the modifier, disintegrating the heat-treated briquettes, subjectingthe disintegrated material in a mould to a pressure of at least about250 atmospheres at a temperature at which under the pressure used themixture softens as a whole without undergoing intumescence, and thenslowly cooling the moulded article.

2. A process as claimed in claim 1, wherein a filling material isincorporated in the mixture of coal and modifier prior to the heattreatment.

3. A process as claimed in claim 1, wherein a filling material isincorporated in the mixture after the heat treatment and prior to themoulding operation.

WALTER IDRIS JONES. DAVID CLARENCE RHYS JONES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,623,588 Germain Apr. 5, 19271,891,893 Spengler et a1 Dec. 20, 1932 2,088,422 Kemmer July 2'7, 19372,404,208 Bangham et a1 July 16, 1946

